At first the Cuban doctors thought they were dealing with an outbreak of food poisoning.

The patients that arrived for treatment in mid-June at hospitals in Manzanillo had all gone to the same birthday party held at a house in the hilly countryside on the perimeter of the eastern Cuban city.

The sick had eaten shrimp at the party and doctors thought that meal might be the cause for the patients' heavy vomiting and diarrhea.

"They started coming in a few at a time," said Julio Cesar Fonseca Rivero, the director of the Celia Sanchez Manduley Hospital, the largest in the region. "The first day five came, and then eight. That's not normal, that five people would come with the same symptoms. The most critical days were when there were 30 to 32 patients who arrived in a single day."

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Casos de cólera en Cuba

A sudden spike in cases of diarrhea is not unusual for Manzanillo's hospitals that treat the surrounding rural communities. There residents often live without indoor plumbing and in the summer months endure the scorching heat and heavy rains.

This summer had already been particularly hot with heavy rains that caused outhouses to flood into several drinking wells.

Still, doctors suspected they were dealing with something they hadn't seen before.

"We became alarmed with the number of cases arriving. We usually see one or two cases of diarrhea each day," said Dr. Oyantis Matos Zamora, who oversees a clinic on the edge of the city that attends to rural residents.

The symptoms some patients exhibited -- the rapid onset of watery diarrhea and dehydration — had also not been seen in generations.

"The way that the outbreak developed and the appearance of other similar cases in the region, we realized this was a problem of a different magnitude," said Dr. Manuel Santin Peña, Cuba's national director of epidemiology.

Cuba's last cholera outbreak occurred over a century ago. Although eradicated in many countries, the disease, according to the World Health Organization, still infects between 3 million and 5 million people each year, killing between 100,000 and 120,000.

In Manzanillo the outbreak has taken on a name of its own. There it's simply referred to by residents as "el evento."

So far "el evento" has taken three lives and infected at least 110 people, said Santin. He said doctors were waiting on test results for tens of other possible cases but said so far fewer than 30% percent of suspected cases had been shown to be cholera.

He denied reports that the Cuban government has underreported the death toll or that the outbreak is spreading to other provinces.

He said a handful of suspected cases had been identified elsewhere in the country. But he said those cases had come from the same region where the original outbreak took place and are believed to have been infected there.

"We can categorically say that there is no other outbreak in any other province," Santin told CNN, outside the entrance to the Celia Sanchez Manduley Hospital, where three more people had arrived suffering from severe diarrhea.

Cuban health officials allowed a CNN crew to be the first media to film in the hospital and speak with doctors there about the ongoing effort to control the cholera outbreak.

To combat the outbreak, the local government has closed 12 contaminated wells around Manzanillo, Santin said. Clean water is being trucked in for residents until a different source of water can be found.

At the entrances to hospitals and government buildings in the city stand buckets for people to wash their hands and soles of their shoes with chlorine bleach.

Kiosks throughout Manzanillo that sell milkshakes, iced drinks or other foods that come into contact with water have been shuttered.

A temporary ban has also been issued for fishing and bathing in waters off the coast that may be contaminated.

While in the rest of the country little has been said in the official press about the cholera, in Granma province, the site of the outbreak, residents are now shown a nightly program on how to prevent infection.

Santin told CNN those efforts appear to be working and that doctors are seeing a decline in the rate of infection. The perception that the outbreak was increasing, he said, came from the seven to 10 days it takes for Cuba's labs to return results of tests on the infected.

"The number of cases is dropping," he said. "That doesn't make us confident so much as make us work to intensify all our preventive measures so that in the next few weeks we can stop the outbreak."

Maria Rosa Rodriguez has seen up close what cholera can do.

The Manzanillo schoolteacher was hospitalized for a week with cholera and only recently was allowed return home to finish her recovery. She winced as she recounted the agony that the infection caused her.

"You're very nervous because we had never seen this before here," Rodriguez said. "You're feeling bad with diarrhea, vomiting and you lose weight very quickly. You think the worst."